1. Field of the Invention
The present invention relates to a drive device, and particularly relates to a drive device for performing electric power conversion by using a switching element.
2. Description of the Background Art
There have been developed lighting devices such as a fluorescent lamp and a street lamp, which use a light-emitting element such as an LED (Light-Emitting Diode). The range of uses of an LED lighting device that uses such an LED has been increased from supplemental lighting to main lighting for household purposes. Generally, the lifetime of a fluorescent lamp is 2 to 3 years, while the lifetime of an LED is approximately 40,000 hours, which is much longer than that of the fluorescent lamp. The LED lighting device is configured with, for example, a plurality of LEDs and a plurality of drive devices for driving these LEDs, respectively.
As an example of the LED lighting device, Japanese Patent Laying-Open No. 2004-207654, for example, discloses a configuration as described below. Specifically, the lighting device includes a rectifier circuit made of a diode bridge, for full-wave rectifying a commercial alternating-current power source (AC 100V), a smoothing circuit made of an electrolytic capacitor, for smoothing a rectified direct current, two LED rows using the smoothed direct current as a common power source and connected in parallel with the relevant common power source, a constant-current circuit connected in series with one of the LED rows, and another constant-current circuit connected in series with the other of the LED rows.
Further, as an example of the LED lighting device, Japanese Patent Laying-Open No. 2004-192833 discloses a configuration as described below. Specifically, this configuration includes two bridge diodes, and an LED unit circuit connected between these bridge diodes. The LED unit circuit includes a smoothing capacitor, which is an electrolytic capacitor.
Replacement of a fluorescent lamp is easy, whereas replacement of an LED lighting device may be difficult because an embedded-type one such as a downlight exists. Accordingly, the LED lighting device is required to have long lifetime.
Here, the LED has long lifetime as described above, and hence in order to prolong the lifetime of the LED lighting device, it is important to prolong the lifetime of the drive device. In the configurations described in Japanese Patent Laying-Open No. 2004-207654 and Japanese Patent Laying-Open No. 2004-192833, a large-capacitance electrolytic capacitor is provided so as to smooth an input alternating-current voltage, after full-wave rectification. However, the lifetime of the electrolytic capacitor is generally short, and is only 5,000 hours under the condition of, for example, 105° C. In addition, such a large-capacitance electrolytic capacitor is large in size, and thus it is difficult to reduce the size of the LED lighting device.